How to send vendor notifications manually on demand
First you will need to create a custom order status, that will not be a part of standard Magento sales order workflow, and enable it in order state "processing".
Edit app/etc/local.xml and add right before the last </config>:
If you have Magento cache enabled, refresh it.
Next, configure uDropship to use this new custom order status to send the notifications to vendors.
Go to System > Configuration > Drop Shipping > Vendor Options. Find Make Available to Dropship on Order Status(es) multiselect, and choose only Ready To Ship status.
Now, when a new order comes in, to notify and make it available for vendors, you will need to change the order status manually to Ready To Ship.
